A powerful magnitude 7.7 earthquake struck off Japan’s northeastern coast on Monday, prompting authorities to urge residents to move away from coastal areas amid warnings of possible tsunami waves reaching up to 3 metres (10 ft).
About two hours after the quake, which hit at 4:53 p.m. local time (0753 GMT), tsunami waves as high as 80 cm had already been observed. Authorities later downgraded the initial tsunami warning to an advisory.
Japan’s Chief Cabinet Secretary, Minoru Kihara, said at a press briefing in Tokyo that there were no immediate reports of deaths or major damage as night fell.
Several coastal towns, including Otsuchi and Kamaishi—areas previously devastated by the 2011 earthquake and tsunami—issued evacuation orders for thousands of residents, according to public broadcaster NHK. Bullet train services were suspended, while sections of major highways were also closed as a precaution.
Following the quake, officials also warned of an increased risk of a larger “megaquake.” A government representative explained that while the probability of a magnitude 8 or stronger earthquake occurring along the Japan Trench and Kuril Trench is typically about 0.1% in any given week, it could rise to around 1% in the week following Monday’s tremor.
“Please take disaster preparedness seriously and act with the mindset of protecting your own life,” the official advised.
The Japan Meteorological Agency (JMA) said the quake was centred in the Pacific Ocean at a depth of about 20 km and registered an “upper 5” on Japan’s seismic intensity scale—strong enough to make movement difficult and potentially cause damage such as the collapse of poorly reinforced walls.
Authorities warned that tsunami waves of up to 3 metres could flood low-lying areas and pose serious risks to anyone caught in the water.
Japan, located along the Pacific “Ring of Fire,” is one of the world’s most earthquake-prone countries, experiencing frequent seismic activity. The country accounts for about 20% of earthquakes measuring magnitude 6.0 or higher globally, including the catastrophic 2011 disaster that triggered nuclear meltdowns at the Fukushima Daiichi power plant.
Despite the strong tremor, officials confirmed there were no abnormalities at idled nuclear facilities in the affected region. Hokkaido Electric Power and Tohoku Electric Power also reported no issues at their plants.